For industrial robots, especially the ones designed to work in limited and complex workspaces, flexibility and compactness are among the major design requirements, and cable routing plays a more and more important role in the applications of robots.
A robot typically comprises one or more rotary joints in order to achieve flexible positioning of robot arms. Generally, the larger the rotation ranges of rotary joints are, the more flexible a robot is. However, in order to transmit power and various signals to and from robot arms, one or more cables typically go through each rotary joint, and these cables cannot bear too much bending and twisting for a long time, which has become one of the major difficulties for large rotation ranges of rotary joints.
In traditional ways, cables or dress packs are routed outside robots, to give the space for cables' bending and prevent them from wearing out. But it will lead to lots of problems. For example, the explosion of robot cables, which are made by common materials, is fatal to vacuum environment of modern cleanrooms, since the out-gassing of cables will pollute the whole workspace and also the products therein. Issues also happen in traditional fields: robots, especially the ones with unprotected robot cables, for machine tending will also suffer from the corrosive cutting fluid, and leads to the reduction of the lifetime of robots and productivity of the plants.
Routing all the wires inside the robot is a new trend nowadays. But due to the limited inner space and requirements of the large bending radius, such kind routing is quite difficult and usually the working ranges of single joints are limited by cable routing rather than other mechanism structures.
Various attempts have been made to solve the problem of routing in limited spaces, and one of the successful solutions is using new materials, such as FPC. Less space needed and longer lifetime makes FPC a preferable routing solution. But due to its nature material characters, FPC is easy to be damaged during the assembly and running of robots, because of contacting projections, sharp edges, burrs, fins, and etc. The insulation on conductors may be abraded, or the FPC could be cut, especially when strain relief structure is not available.
So protections should be adopted when FPC is used in robots.
To wiring through a joint, FPC usually consists two parts: the moving one and the fixed one. In practices, more attentions are paid to the protection of the former one.
To prevent the moving FPC from wearing out by other structures, as shown in FIG. 1A, GB2164506A uses a box which consists of two relatively rotating members to limit the space for FPC and provides smooth contacting surfaces. Following this idea, protections for the moving parts of FPC are extended in JP2009-64479 and JP2012-51045. By adopting such solutions, moving FPC could be well protected. But the fixed parts of FPC could still be damage during assembly.
To give better protection for FPC, DE102011051733 and JP2012035372A try to restrain the whole FPC inside a box by positioning all the connectors on both side of it, as shown in FIG. 1B. This solution is adoptable only when the number of wires of power and signal are limited, otherwise arranging lots of pins or connectors on a single box requires large space, and thus the box will be too big for small and compact robot.
In view of the foregoing, there is a need in the art to develop an improved rotary joint and an improved routing structure.